Planetary gear train of automatic transmission for vehicles

ABSTRACT

A planetary gear train of an automatic transmission for a vehicle improves power delivery and fuel efficiency by applying six control elements to four planetary gear sets to achieve forward nine speed stages and one reverse speed stage. The planetary gear train includes: an input shaft; an output shaft; first to fourth first planetary gear sets each having three rotational element: four clutches and two brakes as the six control elements; and first to ninth shafts. In particular, the first shaft connects a first rotational element and the input shaft; the second shaft is connected with a second rotational element and selectively connected with the first shaft; the third shaft connects third and fifth rotational elements; the fourth shaft is connected with a fourth rotational element and fixed to a transmission housing; and the fourth shaft is connected with the fourth rotational element and fixed to the transmission housing.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2017-0049876, filed on Apr. 18, 2017, which isincorporated herein by reference in its entirety.

FIELD

The present disclosure relates to a planetary gear train of an automatictransmission for a vehicle having advantages of improving power deliveryperformance and fuel consumption.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Generally, in automatic transmission field, achieving more shift stagesis a technology for improving fuel consumption and driving efficiencyand has been researched, and recent increases in oil prices aretriggering hard competition in enhancing fuel consumption of a vehicle.

In this sense, research on an engine has been undertaken to achieveweight reduction and to enhance fuel consumption by so-calleddownsizing, and research on an automatic transmission has been performedto simultaneously provide better drivability and fuel consumption byachieving more shift stages.

In order to achieve more shift stages for an automatic transmission, thenumber of parts, particularly the number of planetary gear sets istypically increased. This negatively affects installability, productioncost, weight, and power flow efficiency, and a total length oftransmission.

The majority of general automatic transmissions having more than eightspeeds also increase its total length, which has drawbacks ofdeteriorating installability.

As a result, plural rows structure which planetary gear sets are onplanetary gear sets has been adopted, or a dog clutch is applied inplace of wet control elements. However, in this case, applicablestructure is restricted and shift feel is deteriorated by applying thedog clutch.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the present disclosureand therefore it may contain information that does not form the priorart that is already known in this country to a person of ordinary skillin the art.

SUMMARY

The present disclosure has been made in an effort to provide a planetarygear train of an automatic transmission for a vehicle having advantagesof obtaining shift-stages of the forward nine speeds and one reversespeed with reduced number of parts, improving power delivery performanceand fuel consumption by multi-stages of an automatic transmission, andimproving driving stability of a vehicle by utilizing a low rotationspeed of an engine.

A planetary gear train according to an exemplary form of the presentdisclosure includes: an input shaft for receiving an engine torque; anoutput shaft for outputting a shifted torque; a first planetary gear sethaving first, second, and third rotational elements; a second planetarygear set having fourth, fifth, and sixth rotational elements; a thirdplanetary gear set having seventh, eighth, and ninth rotationalelements; a fourth planetary gear set having tenth, eleventh, andtwelfth rotational elements; a first shaft connected with the firstrotational element, and connected with the input shaft; a second shaftconnected with the second rotational element and selectively connectedwith the first shaft; a third shaft connected with the third rotationalelement and the fifth rotational element; a fourth shaft connected withthe fourth rotational element and fixed to a transmission housing; afourth shaft connected with the fourth rotational element and fixed to atransmission housing; a sixth shaft connected with the seventhrotational element and the tenth rotational element and selectivelyconnected with the second shaft and fifth shaft respectively; a seventhshaft connected with the eighth rotational element and the twelfthrotational element, and connected with the output shaft; an eighth shaftconnected with the ninth rotational element; and a ninth shaft connectedwith the eleventh rotational element and selectively connected with thefirst shaft.

Further, the second and eighth shafts may be selectively connected withthe transmission housing respectively.

Further, the first, second, and third rotational elements of the firstplanetary gear set may be respectively a first sun gear, a first planetcarrier, and a first ring gear of the first planetary gear set, thefourth, fifth, and sixth rotational elements of the second planetarygear set may be respectively a second sun gear, a second planet carrier,and a second ring gear of the second planetary gear set, the seventh,eighth, and ninth rotational elements of the third planetary gear setmay be respectively a third sun gear, a third planet carrier, and athird ring gear of the third planetary gear set, and the tenth,eleventh, and twelfth rotational elements of the fourth planetary gearset may be respectively a fourth sun gear, a fourth planet carrier, anda fourth ring gear of the fourth planetary gear set.

Further, the planetary gear train may include a first clutch selectivelyconnecting the first shaft and the second shaft; a second clutchselectively connecting the second shaft and the sixth shaft; a thirdclutch selectively connecting the fifth shaft and the sixth shaft; afourth clutch selectively connecting the first shaft and the ninthshaft; a first brake selectively connecting the second shaft and thetransmission housing; and a second brake selectively connecting theeighth shaft and the transmission housing.

A planetary gear train of an automatic transmission for a vehicleaccording to an exemplary form of the present disclosure, shift-stagesof forward nine speeds and one reverse speed may be realized bycombination of four planetary gear sets of simple planetary gear setsand six control elements.

Further, a planetary gear train according to an exemplary form of thepresent disclosure may realize shift stages appropriate for rotationspeed of an engine due to multi-stages of an automatic transmission andimprove driving stability of a vehicle by utilizing a low rotation speedof an engine.

Further, a planetary gear train according to an exemplary form of thepresent disclosure maximize engine driving efficiency by multi-stages ofan automatic transmission, and may improve power delivery performanceand fuel consumption.

Further, effects that can be obtained or expected from exemplary formsof the present disclosure are directly or suggestively described in thefollowing detailed description. That is, various effects expected fromexemplary forms of the present disclosure will be described in thefollowing detailed description.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a planetary gear train according to anexemplary form of the present disclosure; and

FIG. 2 is an operational chart for respective control elements atrespective shift stages in a planetary gear train according to anexemplary form of the present disclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

Hereinafter, an exemplary form of the present disclosure will bedescribed in detail with reference to drawings.

The drawings and description are to be regarded as illustrative innature and not restrictive, and like reference numerals designate likeelements throughout the specification.

In the following description, dividing names of components into first,second, and the like is to divide the names because the names of thecomponents are the same as each other and an order thereof is notparticularly limited.

Further, as used herein, description of elements being “directly”connected or interconnected includes elements that are fixedlyconnected, i.e. one element directly and/or fixedly connected to anotherelement for rotation therewith.

FIG. 1 is a schematic diagram of a planetary gear train according to anexemplary form of the present disclosure.

Referring to FIG. 1, a planetary gear train includes: first, second,third, and fourth planetary gear sets PG1, PG2, PG3, and PG4 arranged ona same axis, an input shaft IS, an output shaft OS, nine shafts TM1 toTM9 connected with rotational elements of the first, second, third, andfourth planetary gear sets PG1, PG2, PG3, and PG4, four clutches C1 toC4 and two brakes B1 and B2 as control elements, and a transmissionhousing H.

Torque input from the input shaft IS is shifted by cooperative operationof the first, second, third, and fourth planetary gear sets PG1, PG2,PG3, and PG4, and then output through the output shaft OS.

The simple planetary gear sets are arranged in the order of first,second, third and fourth planetary gear sets PG1, PG2, PG3 and PG4, froman engine side.

The input shaft IS is an input member and the torque from a crankshaftof an engine, after being torque-converted through a torque converter,is input into the input shaft IS.

The output shaft OS is an output member, and being arranged on a sameaxis with the input shaft IS, delivers a shifted torque to a drive shaftthrough a differential apparatus which is not illustrated.

The first planetary gear set PG1 is a single pinion planetary gear set,and includes a first sun gear S1, a first planet carrier PC1 thatsupports a plurality of first pinion gear P1 externally engaged with thefirst sun gear S1 so that the first pinion gear P1 may rotate andrevolute, and a first ring gear R1 internally engaged andtorque-connected with a plurality of the first pinion gear P1. The firstsun gear S1 acts as a first rotational element N1, the first planetcarrier PC1 acts as a second rotational element N2, and the first ringgear R1 acts as a third rotational element N3.

The second planetary gear set PG2 is a single pinion planetary gear set,and includes a second sun gear S2, a second planet carrier PC2 thatsupports a plurality of second pinion gear P2 externally engaged withthe second sun gear S2 so that the second pinion gear P2 may rotate andrevolute, and a second ring gear R2 internally engaged andtorque-connected with a plurality of the second pinion P2. The secondsun gear S2 acts as a fourth rotational element N4, the second planetcarrier PC2 acts as a fifth rotational element N5, and the second ringgear R2 acts as a sixth rotational element N6.

The third planetary gear set PG3 is a single pinion planetary gear set,and includes a third sun gear S3, a third planet carrier PC3 thatsupports a plurality of a third pinion gear P3 externally engaged withthe third sun gear S3 so that the third pinion gear P3 may rotate andrevolute, and a third ring gear R3 internally engaged andtorque-connected with a plurality of the third pinion P3. The third sungear S3 acts as a seventh rotational element N7, the third planetcarrier PC3 acts as a eighth rotational element N8, and the third ringgear R3 acts as a ninth rotational element N9.

The fourth planetary gear set PG4 is a single pinion planetary gear set,and includes a fourth sun gear S4, a fourth planet carrier PC4 thatsupports a plurality of a fourth pinion gear P4 externally engaged withthe fourth sun gear S4 so that the fourth pinion gear P4 may rotate andrevolute, and a fourth ring gear R4 internally engaged andtorque-connected with a plurality of the fourth pinion P4. The fourthsun gear S4 acts as a tenth rotational element N10, the fourth planetcarrier PC4 acts as a eleventh rotational element N11, and the fourthring gear R4 acts as a twelfth rotational element N12.

In the arrangement of the first, second, third, and fourth planetarygear sets PG1, PG2, PG3, and PG4, the third rotational element N3 andthe fifth rotational element N5 are directly connected with each other,the seventh rotational element N7 and the tenth rotational element N10are directly connected with each other, and the eighth rotationalelement N8 and the twelfth rotational element N12 are directly connectedwith each other by a corresponding shaft selected from the nine shaftsTM1 to TM9.

The nine shafts TM1 to TM9 are arranged as follows.

Each of the nine shafts TM1 to TM9 may be a rotational member thatdelivers torque and rotates with rotational element via directly orselectively interconnecting a plurality of the rotational elements ofthe rotational elements of the planetary gear sets PG1, PG2, PG3, andPG4, and the nine shafts TM1 to TM9 may be a rotational memberselectively connecting the rotational element with the transmissionhousing H, or be a fixed member directly connecting and fixing therotational element(s) with the transmission housing H.

The first shaft TM1 directly connects the first rotational element N1(the first sun gear S1) and is directly connected with the input shaftIS, thereby always acting as an input element.

The second shaft TM2 is connected, and preferably fixedly connected,with the second rotational element N2 (the first planet carrier PC1),selectively connected with the first shaft TM1, and selectivelyconnected with the transmission housing H, thereby acting as a selectivefixed element.

The third shaft TM3 is connected, and preferably fixedly connected, withthe third rotational element N3 (the first ring gear R1) and the fifthrotational element N5 (the second planet carrier PC2).

The fourth shaft TM4 is connected, and preferably fixedly connected,with the fourth rotational element N4 (the second sun gear S2), anddirectly connected with the transmission housing H, thereby alwaysacting as a fixed element.

The fifth shaft TM5 is connected, and preferably fixedly connected, withthe sixth rotational element N6 (the second ring gear R2).

The sixth shaft TM6 is connected, and preferably fixedly connected, withthe seventh rotational element N7 (the third sun gear S3) and the tenthrotational element N10 (the fourth sun gear S4) and selectivelyconnected with the second shaft TM2 and the fifth shaft TM5.

The seventh shaft TM7 is connected, and preferably fixedly connected,with the eighth rotational element N8 (the third planetary carrier PC3)and the twelfth rotational element N12 (the fourth ring gear R4), andconnected with the output shaft OS, thereby always acting as an outputelement.

The eighth shaft TM8 is connected, and preferably fixedly connected,with the ninth rotational element N9 (the third ring gear R3), andselectively connected with the transmission housing H, thereby acting asa selective fixed element.

The ninth shaft TM9 is connected, and preferably fixedly connected, withthe eleventh rotational element N11 (the fourth planetary carrier PC4),and selectively connected with the first shaft TM1.

The nine shafts TM1 to TM9, the input shaft IS, and the output shaft OSmay be selectively interconnected with one another by control elementsof four clutches C1, C2, C3 and C4.

The shafts TM1 to TM9 may be selectively connected with the transmissionhousing H, by control elements of two brakes B1 and B2.

The four clutches C1 to C4 and the two brakes B1 and B2 are arranged asfollows.

The first clutch C1 is arranged between the first shaft TM1 and thesecond shaft TM2, so as to selectively connect the first shaft TM1 andthe second shaft TM2 for power delivery.

The second clutch C2 is arranged between the second shaft TM2 and thesixth shaft TM6, so as to selectively connect the second shaft TM2 andthe sixth shaft TM6 for power delivery.

The third clutch C3 is arranged between the fifth shaft TM5 and thesixth shaft TM6, so as to selectively connect the fifth shaft TM5 andthe sixth shaft TM6 for power delivery.

The fourth clutch C4 is arranged between the first shaft TM1 and theninth shaft TM9, so as to selectively connect the first shaft TM1 andthe ninth shaft TM9 for power delivery.

The first brake B1 is arranged between the second shaft TM2 and thetransmission housing H, such that the second shaft TM2 may beselectively connected with the transmission housing H and act as a fixedelement.

The second brake B2 is arranged between the eighth shaft TM3 and thetransmission housing H, such that the eighth shaft TM8 may beselectively connected with the transmission housing H and act as a fixedelement.

The control elements of the first, second, third, and fourth clutchesC1, C2, C3, and C4 and the first and second brakes B1 and B2 may berealized as hydraulic pressure friction control elements that arefrictionally engaged by hydraulic pressure supplied from a hydraulicpressure control devices. The control elements are primarily used as awet multi-plate hydraulic pressure friction control element, but ascontrol elements which may operate according to electric signal suppliedfrom an electronic control devices such as a dog clutch, anelectro-magnetic clutch, a magna clutch etc.

FIG. 2 is an operational chart for respective control elements atrespective shift stages in a planetary gear train according to anexemplary form of the present disclosure.

Referring to FIG. 2, a planetary gear train realizes forward nine speedsand one reverse speed by operating three control elements among thefirst, second, third, and fourth clutches C1, C2, C3, and C4 and thefirst and second brakes B1 and B2 at respective shift-stages.

In the forward first speed shift-stage D1, the second and third clutchesC2 and C3 and the second brake B2 are simultaneously operated.

As a result, the second shaft TM2 and the sixth shaft TM6 areinterconnected with each other by the operation of the second clutch C2,and the fifth shaft TM5 and the sixth shaft TM6 are interconnected witheach other by the operation of the third clutch C3. In this state,torque of the Input shaft IS is input to the first shaft TM1.

Further, the eighth shaft TM8 acts as a fixed element by the operationof the second brake B2, thereby realizing the forward first speed andoutputting a shifted torque through the output shaft OS connected withthe seventh shaft TM7.

In the forward second speed shift-stage D2, the first and secondclutches C1 and C2 and the second brake B2 are simultaneously operated.

As a result, the first shaft TM1 and the second shaft TM2 areinterconnected with each other by the operation of the first clutch C1,and the second shaft TM2 and the sixth shaft TM6 are interconnected witheach other by the operation of the second clutch C2. In this state,torque of the Input shaft IS is input to the first shaft TM1.

Further, the eighth shaft TM8 acts as a fixed element by the operationof the second brake B2, thereby realizing the forward second speed andoutputting a shifted torque through the output shaft OS connected withthe seventh shaft TM7.

In the forward third speed shift-stage D3, the first and third clutchesC1 and C3 and the second brake B2 are simultaneously operated.

As a result, the first shaft TM1 and the second shaft TM2 areinterconnected with each other by the operation of the first clutch C1,and the fifth shaft TM5 and the sixth shaft TM6 are interconnected witheach other by the operation of the third clutch C3. In this state,torque of the Input shaft IS is input to the first shaft TM1.

Further, the eighth shaft TM8 acts as a fixed element by the operationof the second brake B2, thereby realizing the forward third speed andoutputting a shifted torque through the output shaft OS connected withthe seventh shaft TM7.

In the forward fourth speed shift-stage D4, the first and fourthclutches C1 and C4 and the second brake B2 are simultaneously operated.

As a result, the first shaft TM1 and the second shaft TM2 areinterconnected with each other by the operation of the first clutch C1,and the sixth shaft TM6 and the ninth shaft TM9 are interconnected witheach other by the operation of the fourth clutch C4. In this state,torque of the Input shaft IS is input to the first shaft TM1.

Further, the eighth shaft TM8 acts as a fixed element by the operationof the second brake B2, thereby realizing the forward fourth speed andoutputting a shifted torque through the output shaft OS connected withthe seventh shaft TM7.

In the forward fifth speed shift-stage D5, the first, third, and fourthclutches C1, C3, and C4 are simultaneously operated.

As a result, the first shaft TM1 and the second shaft TM2 areinterconnected with each other by the operation of the first clutch C1,the fifth shaft TM5 and the sixth shaft TM6 are interconnected with eachother by the operation of the third clutch C3, and the first shaft TM1and the ninth shaft TM9 are interconnected with each other by theoperation of the fourth clutch C4. In this state, torque of the Inputshaft IS is input to the first shaft TM1.

Then, the forward fifth speed is realized and a shifted torque throughthe output shaft OS connected with the seventh shaft TM7 is output.

In the forward sixth speed shift-stage D6, the first, second, and fourthclutches C1, C2, and C4 are simultaneously operated.

As a result, the first shaft TM1 and the second shaft TM2 areinterconnected with each other by the operation of the first clutch C1,the second shaft TM2 and the sixth shaft TM6 are interconnected witheach other by the operation of the second clutch C2, and the first shaftTM1 and the ninth shaft TM9 are interconnected with each other by theoperation of the fourth clutch C4. In this state, torque of the Inputshaft IS is input to the first shaft TM1.

Then, the first, second, third, and fourth planetary gear sets PG1, PG2,PG3, and PG4 are integrally rotate, and a shifted torque of the inputshaft IS is transmitted to a forward sixth speed to be output throughthe output shaft OS connected with the seventh shaft TM7.

In the forward sixth speed shift-stage D7, the second, third, and fourthclutches C2, C3, and C4 are simultaneously operated.

As a result, the second shaft TM2 and the sixth shaft TM6 areinterconnected with each other by the operation of the second clutch C2,the fifth shaft TM5 and the sixth shaft TM6 are interconnected with eachother by the operation of the third clutch C3, and the first shaft TM1and the ninth shaft TM9 are interconnected with each other by theoperation of the fourth clutch C4. In this state, torque of the Inputshaft IS is input to the first shaft TM1.

Then, the forward seventh speed is realized and a shifted torque throughthe output shaft OS connected with the seventh shaft TM7 is output.

In the forward eighth speed shift-stage D8, the second and fourthclutches C2 and C4 and the first brake B1 are simultaneously operated.

As a result, the second shaft TM2 and the sixth shaft TM6 areinterconnected with each other by the operation of the second clutch C2,and the first shaft TM1 and the ninth shaft TM9 are interconnected witheach other by the operation of the fourth clutch C4. In this state,torque of the Input shaft IS is input to the first shaft TM1.

Further, the second shaft TM2 acts as a fixed element by the operationof the first brake B1, thereby realizing the forward eighth speed andoutputting a shifted torque through the output shaft OS connected withthe seventh shaft TM7.

In the forward ninth speed shift-stage D9, the third and fourth clutchesC3 and C4 and the first brake B1 are simultaneously operated.

As a result, the fifth shaft TM5 and the sixth shaft TM6 areinterconnected with each other by the operation of the third clutch C3,and the first shaft TM1 and the ninth shaft TM9 are interconnected witheach other by the operation of the fourth clutch C4. In this state,torque of the Input shaft IS is input to the first shaft TM1.

Further, the second shaft TM2 acts as a fixed element by the operationof the first brake B1, thereby realizing the forward ninth speed andoutputting a shifted torque through the output shaft OS connected withthe seventh shaft TM7.

In the reverse speed REV, the third clutch C3, the first and secondbrakes B1 and B2 are simultaneously operated.

As a result, the fifth shaft TM5 and the sixth shaft TM6 areinterconnected by the operation of the third clutch C3. In this state,torque of the Input shaft IS is input to the first shaft TM1.

Further, the second shaft TM2 and the eighth shaft TM8 act as fixedelements by the operation of the first brake B1 and the second brake B2,thereby realizing the reverse speed and outputting a shifted torquethrough the output shaft OS connected with the seventh shaft TM7.

As described above, a planetary gear train according to an exemplaryform of the present disclosure may realize forward nine speeds and areverse first speed formed by operating four planetary gear sets PG1,PG2, PG3, and PG4 by controlling the four clutches C1, C2, C3, and C4and the two brakes B1 and B2.

In addition, a planetary gear train according to an exemplary form ofthe present disclosure may realize shift stages appropriate for rotationspeed of an engine due to multi-stages of an automatic transmission andimprove driving stability of a vehicle by utilizing a low rotation speedof an engine.

In addition, a planetary gear train according to an exemplary form ofthe present disclosure may increase engine driving efficiency bymulti-stages of an automatic transmission, and may improve powerdelivery performance and fuel consumption.

While this present disclosure has been described in connection with whatis presently considered to be practical exemplary forms, it is to beunderstood that the present disclosure is not limited to the disclosedforms, but, on the contrary, is intended to cover various modificationsand equivalent arrangements included within the spirit and scope of thepresent disclosure.

DESCRIPTION OF SYMBOLS

-   -   B1, B2 . . . first and second brakes    -   C1, C2, C3, C4 . . . first, second, third, and fourth clutches    -   PG1, PG2, PG3, PG4 . . . first, second, third, and fourth        planetary gear sets    -   S1, S2, S3, S4 . . . first, second, third, and fourth sun gears    -   PC1, PC2, PC3, PC4 . . . first, second, third, and fourth planet        carriers    -   R1, R2, R3, R4 . . . first, second, third, and fourth ring gears    -   IS . . . input shaft    -   OS . . . output shaft    -   TM1, TM2, TM3, TM4, TM5, TM6, TM7, TM8, TM9 . . . first, second,        third, fourth, fifth, sixth, seventh, eighth, and ninth shafts

What is claimed is:
 1. A planetary gear train of an automatictransmission for a vehicle, the planetary gear train comprising: aninput shaft configured to receive an engine torque; an output shaftconfigured to output a shifted torque; a first planetary gear set havingfirst, second, and third rotational elements; a second planetary gearset having fourth, fifth, and sixth rotational elements; a thirdplanetary gear set having seventh, eighth, and ninth rotationalelements; a fourth planetary gear set having tenth, eleventh, andtwelfth rotational elements; a first shaft connected with the firstrotational element, and connected with the input shaft; a second shaftconnected with the second rotational element and selectively connectedwith the first shaft; a third shaft connected with the third rotationalelement and the fifth rotational element; a fourth shaft connected withthe fourth rotational element and fixed to a transmission housing; afifth shaft connected with the sixth rotational element; a sixth shaftconnected with the seventh rotational element and the tenth rotationalelement and selectively connected with the second shaft and the fifthshaft respectively; a seventh shaft connected with the eighth rotationalelement and the twelfth rotational element, and connected with theoutput shaft; an eighth shaft connected with the ninth rotationalelement; and a ninth shaft connected with the eleventh rotationalelement and selectively connected with the first shaft.
 2. The planetarygear train of claim 1, wherein the second and eighth shafts areselectively connected with the transmission housing respectively.
 3. Theplanetary gear train of claim 1, wherein the first, second, and thirdrotational elements of the first planetary gear set are respectively afirst sun gear, a first planet carrier, and a first ring gear of thefirst planetary gear set, the fourth, fifth, and sixth rotationalelements of the second planetary gear set are respectively a second sungear, a second planet carrier, and a second ring gear of the secondplanetary gear set, the seventh, eighth, and ninth rotational elementsof the third planetary gear set are respectively a third sun gear, athird planet carrier, and a third ring gear of the third planetary gearset, and the tenth, eleventh, and twelfth rotational elements of thefourth planetary gear set are respectively a fourth sun gear, a fourthplanet carrier, and a fourth ring gear of the fourth planetary gear set.4. The planetary gear train of claim 2, wherein the planetary gear trainincludes a first clutch configured to selectively connect the firstshaft and the second shaft; a second clutch configured to selectivelyconnect the second shaft and the sixth shaft; a third clutch configuredto selectively connect the fifth shaft and the sixth shaft; a fourthclutch configured to selectively connect the first shaft and the ninthshaft; a first brake configured to selectively connect the second shaftand the transmission housing; and a second brake configured toselectively connect the eighth shaft and the transmission housing.
 5. Aplanetary gear train of an automatic transmission for a vehicle, theplanetary gear train comprising: an input shaft configured to receive anengine torque; an output shaft configured to output a shifted torque; afirst planetary gear set having first, second, and third rotationalelements; a second planetary gear set having fourth, fifth, and sixthrotational elements; a third planetary gear set having seventh, eighth,and ninth rotational elements; and a fourth planetary gear set havingtenth, eleventh, and twelfth rotational elements, wherein the inputshaft is connected with the first rotational element, the output shaftis connected with the twelfth rotational element, the third rotationalelement is connected with the fifth rotational element, the fourthrotational element is connected with a transmission housing, the seventhrotational element is connected with the tenth rotational element, theeighth rotational element is connected with the twelfth rotationalelement, the first rotational element is selectively connected with theeleventh rotational element, the second rotational element isselectively connected with the first and seventh rotational elementsrespectively, and the sixth rotational element is selectively connectedwith the seventh rotational element.
 6. The planetary gear train ofclaim 5, wherein the second and ninth rotational elements areselectively connected with the transmission housing respectively.
 7. Theplanetary gear train of claim 5, wherein the first, second, and thirdrotational elements of the first planetary gear set are respectively afirst sun gear, a first planet carrier, and a first ring gear of thefirst planetary gear set, the fourth, fifth, and sixth rotationalelements of the second planetary gear set are respectively a second sungear, a second planet carrier, and a second ring gear of the secondplanetary gear set, the seventh, eighth, and ninth rotational elementsof the third planetary gear set are a third sun gear, a third planetcarrier, and a third ring gear of the third planetary gear set, and thetenth, eleventh, and twelfth rotational elements of the fourth planetarygear set are respectively a fourth sun gear, a fourth planet carrier,and a fourth ring gear of the fourth planetary gear set.
 8. Theplanetary gear train of claim 6, wherein the planetary gear trainincludes a first clutch configured to selectively connect the firstrotational element and the second rotational element; a second clutchconfigured to selectively connect the second rotational element and theseventh rotational element; a third clutch configured to selectivelyconnect the sixth rotational element and the seventh rotational element;a fourth clutch configured to selectively connect the first rotationalelement and the eleventh rotational element; a first brake configured toselectively connect the second rotational element and the transmissionhousing; and a second brake configured to selectively connect the ninthrotational element and the transmission housing.